In a typical consumable electrode arc welding, welding is performed by feeding a welding wire as a consumable electrode at a constant feeding rate and generating an arc between the welding wire and base material. In the consumable electrode arc welding, both the welding wire and the base material are mostly placed in a welding state in which a short-circuiting period and an arc period are alternately repeated.
In order to further improve welding quality, there has been proposed a welding method of alternating feeding of the welding wire between forward feeding and reverse feeding periodically (see Patent Document 1, for example). Hereinafter this welding method will be explained.
FIG. 4 is a waveform diagram of the welding method in which the forward feeding and the reverse feeding are alternated periodically as to a feeding rate. (A) of this figure shows a waveform of a feeding rate Fw, (B) of this figure shows a waveform of a welding current Iw and (C) of this figure shows a waveform of a welding voltage Vw. Hereinafter explanation will be made with reference to this figure.
As shown in (A) of this figure, in the feeding rate Fw, an upper side and a lower side than 0 represent a forward feeding period and a reverse feeding period, respectively. The forward feeding represents feeding of the welding wire in a direction approaching the base material, whilst the reverse feeding represents feeding of the welding wire in a direction separating from the base material. The feeding rate Fw has a waveform which changes sinusoidalty and shifts on the forward feeding side. Thus as an average value of the feeding rate Fw is positive, the welding wire is fed forwardly in average.
As shown in (A) of this figure, the feeding rate Fw is 0 at a time t1. A period from the time t1 to a time t2 corresponds to a forward feeding acceleration period. The feeding rate is the maximum value of the forward feeding at the time t2. A period from the time t2 to a time t3 corresponds to a forward feeding deceleration period. The feeding rate is 0 at the time t3. A period from the time t3 to a time t4 corresponds to a reverse feeding acceleration period. The feeding rate is the maximum value of the reverse feeding at the time t4. A period from the time t4 to a time t5 corresponds to a reverse feeding deceleration period. Then a period from the time t5 to a time t6 is the forward feeding acceleration period again, and a period from the time t6 to a time t7 is the forward feeding deceleration period again. Thus the feeding rate Fw periodically changes according to a feeding rate pattern. This pattern is constituted of a cycle Tf (ms) from the time t1 to the time t5, an amplitude Wf (mm/min) as a difference between the maximum value of the forward feeding at the time t2 and the maximum value of the reverse feeding at the time t4 and a forward-feeding side shift amount Sf (mm/min) which are respectively set to individual predetermined values.
Short circuit between the welding wire and the base material occurs mostly before or after the maximum value of the forward feeding at the time t2. This figure shows a case where the short circuit occurs at a time t21 in the forward feeding deceleration period after the maximum value of the forward feeding. If the short circuit occurs at the time t21, the welding voltage Vw rapidly reduces to a short-circuit voltage value of a few volts as shown in (C) of this figure, whilst the welding current Iw increases gradually as shown in (B) of this figure.
As shown in (A) of this figure, from the time t3, as the feeding rate Fw is placed in the reverse feeding period, the welding wire is reversely fed. The short circuit is released by this reverse feeding, and hence an arc is regenerated at a time t31. The arc is regenerated mostly before or after the maximum value of the reverse feeding at the time t4. This figure shows a case where the arc is generated at the time t31 in the reverse feeding acceleration period before the peak value of the reverse feeding. Thus a time period from the time t21 to the time t31 corresponds to the short-circuiting period.
If the arc is regenerated at the time t31, the welding voltage Vw increases rapidly to an arc voltage value of several tens of volts as shown in (C) of this figure. As shown in (B) of this figure, the welding current Iw starts changing from the maximum value state in the short-circuiting period.
As shown in (A) of this figure, during a period from the time t31 to the time t5, as the feeding rate Fw is in the reverse feeding state, the welding wire is raised and hence a length of the arc becomes longer gradually. If the arc length becomes longer, the welding voltage Vw increases, and hence the welding current Iw reduces due to a constant voltage control. Thus during a reverse feeding period Tar in the arc period from the time t31 to the time t5, the welding voltage Vw increases gradually as shown in (C) of this figure, whilst the welding current Iw reduces gradually as shown in (B) of this figure.
Then the next short circuit occurs at a time t61 within the forward feeding deceleration period from the time t6 to the time t7, The short circuit occurred at the time t61 is later in a time (phase) from the maximum value of the forward feeding than the short circuit occurred at the time t21. In this manner, the occurrence timing of short circuit has a certain degree of valiance. A time period from the time t31 to the time t61 corresponds to the arc period. As shown in (A) of this figure, during a period from the time t5 to the time t61, as the feeding rate Fw is in the forward feeding state, the welding wire is forwardly fed and hence a length of the arc becomes shorter gradually. If the arc length becomes shorter, the welding voltage Vw reduces, and hence the welding current Iw increases due to the constant voltage control. Thus during a forward feeding period Tas in the arc period from the time t5 to the time t61, the welding voltage Vw reduces gradually as shown in (C) of this figure, whilst the welding current Iw increases gradually as shown in (B) of this figure.
As described above, in the welding method of repeating the forward feeding and the reverse feeding of the welding wire alternately, the repetition cycle of short circuit and arc can be set to a desired value despite that such the setting is impossible in the related art of the feeding at a constant feeding rate. Thus a generation amount of spatter can be reduced, and improvement of welding quality such as improvement of bead appearance can be achieved.
According to the invention of the patent document 1, an average value of the feeding rate is adjusted according to a welding current setting value, and a repetition frequency and an amplitude of the forward feeding and the reverse feeding of the welding wire are adjusted to individual values according to the welding current setting value. As a result, welding can be performed stably even if the welding current setting value changes.